Alison Reay, joint managing director at Titan, said the company had hired 112 people across all departments since rebranding as Titan Outdoor a year ago and increased the total headcount by 32.
She said: "Developing teams of this calibre doesn't happen overnight, but now these people are in place we're geared up to be a very focused and energetic team."
Reay stressed the company was "looking to the future, not looking back" and described the number of people who have joined the company in the last year as "phenomenal".
Stephen Dunn has been named sales director, leaving his role as deputy managing director and sales director for Titan in Ireland, while The Guardian's David Etherington will become marketing director.
Titan bosses have teamed up Dunn's outdoor expertise with Etherington's experience in multiplatform selling, gained through his work in Guardian Plus, a division of The Guardian's sales team that specialises in sponsorship and promotions.
Clear Channel's Laura Thompson has been made a group head of Titan+, the division launched at the end of 2006 to offer integrated campaigns across landmark, experience and digital.
She will initially focus on the new rail corridor sponsorship and station domination opportunities, before moving on to head the landmark and experience teams in Titan+.
Colette Lister takes up the role of sales operations director, overseeing behind-the-scenes customer service, as well as managing sales and inventory processes, and Ged Weston has been promoted internally to the role of director for specialist sales.
Lister joins from GCap Media where she worked most recently as trading and operations director, overseeing its merger restructure, while Weston has worked across all areas of sales during his seven years with Titan, developing an extensive knowledge of sales operations and outdoor.
Matt Johnston has also been named chief financial officer, while John Wolstenholme becomes acting roadside commercial director.
Recent high-profile defections to rival CBS include development director Helen Bouchez and research director Anthony Waithe, while sales director Steve Atkinson also departed this year.